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[2620:137:e000::1:20]) by mx.google.com with ESMTP id hg9-20020a17090b300900b0024bc03cfa95si1694676pjb.156.2023.06.01.15.35.34; Thu, 01 Jun 2023 15:35:45 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@invisiblethingslab.com header.s=fm1 header.b=Z4CU56Am; dkim=pass header.i=@messagingengine.com header.s=fm1 header.b=Scu4bR1S; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233016AbjFAW1D (ORCPT + 99 others); Thu, 1 Jun 2023 18:27:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46296 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233059AbjFAW1C (ORCPT ); Thu, 1 Jun 2023 18:27:02 -0400 Received: from out3-smtp.messagingengine.com (out3-smtp.messagingengine.com [66.111.4.27]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 25D40133; Thu, 1 Jun 2023 15:27:01 -0700 (PDT) Received: from compute1.internal (compute1.nyi.internal [10.202.2.41]) by mailout.nyi.internal (Postfix) with ESMTP id 917AE5C00E9; Thu, 1 Jun 2023 18:27:00 -0400 (EDT) Received: from mailfrontend1 ([10.202.2.162]) by compute1.internal (MEProxy); Thu, 01 Jun 2023 18:27:00 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= invisiblethingslab.com; h=cc:cc:content-transfer-encoding :content-type:date:date:from:from:in-reply-to:message-id :mime-version:reply-to:sender:subject:subject:to:to; s=fm1; t= 1685658420; x=1685744820; bh=iy/GUaaPPTaS6rwFy0PBDtNgCO5kwW/eHTt pnmc0zuM=; b=Z4CU56AmPFLmSjNIWicm+SUnvn06uYZdblO+4TbIMCkPjvv3Ln1 PUGtE16bSWofN22Vt+X2zZGIJGkuyouG/D5XPX8FvyTvcTrnvhzAuXCfY6ReCRCg DiP6PNnaBxDU3OKY+F4z5pvJd1q5JvD5Kro6Nm/M3m6hYgGN7smjJSFilEt8t4zB COaptwSpXohvxx2Gtb4UQ9U3UD7gU6gielaRyN58klN5CzFW+a4rUrI76DvkM/tR wZV1J7+zVS+99LLzT780Rgd8aVgzRUqggLcsEDZyEIBXZ/5V9Vfr0VueVc3fKVGe Rr1JnCq40cUvesA+lXIWJiE4XaxF4hbYslQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-transfer-encoding :content-type:date:date:feedback-id:feedback-id:from:from :in-reply-to:message-id:mime-version:reply-to:sender:subject :subject:to:to:x-me-proxy:x-me-proxy:x-me-sender:x-me-sender :x-sasl-enc; s=fm1; t=1685658420; x=1685744820; bh=iy/GUaaPPTaS6 rwFy0PBDtNgCO5kwW/eHTtpnmc0zuM=; b=Scu4bR1SCTs286aPBJ/DD1KjDzD/I 8RxwId/3DCAKrMCzel/o2GuBy11qjd0/saTJzkxC9YQ7W5i1HQkQgsZYDNDkhKCc 1ktSFIQWP/HgA3TwfskAKrmbngIVbgpj58M3qeHRQw/8A+6Fuszl+N0TNADd2cOS DmYiSHJgB/XGiYuIRG7aUyOQWrU5IQ6B0gutiBrATt9WODw73zImss9wLnbj43ow Hxb7d9FRjkaeHWMu4VA+TXX273Q2GbSvRIEuOMqeNbRbRW+FXLCND3HiDlQdGQSJ fPyGd0o/NyhaV82tXsUsGqbTlPt20GIaDtNlTHL5YZlq9YMXvOtJmdiAg== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvhedrfeelvddguddtucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhephffvvefufffkofgggfestdekredtredttdenucfhrhhomhepffgvmhhiucfo rghrihgvucfqsggvnhhouhhruceouggvmhhisehinhhvihhsihgslhgvthhhihhnghhslh grsgdrtghomheqnecuggftrfgrthhtvghrnhepvdefgeekvdekgfffgeekhfeijedtffek hefhleehfeejueetgfelgefgtdevieelnecuvehluhhsthgvrhfuihiivgeptdenucfrrg hrrghmpehmrghilhhfrhhomhepuggvmhhisehinhhvihhsihgslhgvthhhihhnghhslhgr sgdrtghomh X-ME-Proxy: Feedback-ID: iac594737:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 1 Jun 2023 18:26:59 -0400 (EDT) From: Demi Marie Obenour To: Jens Axboe Cc: Demi Marie Obenour , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] block, loop: Increment diskseq when releasing a loop device Date: Thu, 1 Jun 2023 18:26:56 -0400 Message-Id: <20230601222656.2062-1-demi@invisiblethingslab.com> X-Mailer: git-send-email 2.40.1 MIME-Version: 1.0 X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW,SPF_HELO_PASS, SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1767541514804269396?= X-GMAIL-MSGID: =?utf-8?q?1767541514804269396?= The previous patch for checking diskseq in blkback is not enough to prevent the following race: 1. Program X opens a loop device 2. Program X gets the diskseq of the loop device. 3. Program X associates a file with the loop device. 4. Program X passes the loop device major, minor, and diskseq to something. 5. Program X exits. 6. Program Y detaches the file from the loop device. 7. Program Y attaches a different file to the loop device. 8. The opener finally gets around to opening the loop device and checks that the diskseq is what it expects it to be. Even though the diskseq is the expected value, the result is that the opener is accessing the wrong file. To prevent this race condition, increment the diskseq of a loop device when it is detached from its file descriptor. This causes blkback (or any other program, for that matter) to fail at step 8. Export the inc_diskseq() function to make this possible. Signed-off-by: Demi Marie Obenour --- I considered destroying the loop device altogether instead of bumping its diskseq, but was not able to accomplish that. Suggestions welcome. --- block/genhd.c | 1 + drivers/block/loop.c | 6 ++++++ 2 files changed, 7 insertions(+) diff --git a/block/genhd.c b/block/genhd.c index 1cb489b927d50ab06a84a4bfd6913ca8ba7318d4..c0ca2c387732171321555cd57565fbc606768505 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -1502,3 +1502,4 @@ void inc_diskseq(struct gendisk *disk) { disk->diskseq = atomic64_inc_return(&diskseq); } +EXPORT_SYMBOL(inc_diskseq); diff --git a/drivers/block/loop.c b/drivers/block/loop.c index bc31bb7072a2cb7294d32066f5d0aa14130349b4..05ea5fb41508b4106f184dd6b4c37942716bdcac 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1205,6 +1205,12 @@ static void __loop_clr_fd(struct loop_device *lo, bool release) if (!part_shift) set_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state); mutex_lock(&lo->lo_mutex); + + /* + * Increment the disk sequence number, so that userspace knows this + * device now points to something else. + */ + inc_diskseq(lo->lo_disk); lo->lo_state = Lo_unbound; mutex_unlock(&lo->lo_mutex);